In the manufacture of integrated circuit (IC) devices, a semiconductor substrate, such as a silicon wafer, is processed by placing the substrate through any number of process steps. Such steps include deposition steps, removal steps, patterning steps (e.g., photolithography), and doping. In many instances, material is removed, added, or modified by exposing the substrate to a chemical for a period of time. In addition, there may be cleaning and rinsing steps to remove residue of the chemical left on the substrate, which could damage the device if allowed to remain.
As IC device features continue to decrease in size, existing methods for processing wafers by exposing the wafers to liquid chemicals have become inadequate. For example, a traditional immersion method, whereby a substrate is submerged in a liquid chemical, such as an organic solvent chemical or wet etching chemical, does not provide sufficient control over contact time between the substrate and the chemical. For example, the upper portion of the substrate may be the last to be lowered into the chemical and the first to be lifted out from the chemical. Furthermore, after being raised out of the chemical, the substrate may still have a layer of chemical adhered to the surface of the substrate for some time until the substrate can be moved to a rinsing and drying station. It would be desirable to more precisely control the contact time and the time to rinse.
In addition, substrate immersion does not provide an efficient use of the chemicals. For example, immersion requires significantly more chemical liquid than necessary to carry out the desired chemical reaction or process. In some instances, this liquid cannot be reused, or can only be reused a limited number of times. It would therefore be desirable to reduce the amount of chemical usage for a given process.
Finally, immersion techniques are amenable to batch processing, wherein a number of substrates are lowered into the chemical at the same time. While this improves the efficiency of the immersion technique, it requires additional handling of the substrate to load a number of substrates into a tray and then unload them. Each time a substrate is handled, i.e., moved from one process station to the next, it delays the time to the next process step. In addition, a time delay between removal of a substrate from a chemical and washing, rinsing, and drying operations can vary when a number of substrates are removed at once, but then are further processed only one at a time. It would be desirable to handle a substrate fewer times, and to provide for more consistent handling of substrates from one substrate to the next.
To overcome the advantages noted above, there is a need for improved mechanisms for treatment of a substrate with a liquid chemical.